Since the early 1970's, two main Hot Dry Rock geothermal energy projects are in progress. The first one, at Fenton Hill(USA), has been carried out by the Los Alamos National Laboratory (Mock J., 1989). Three boreholes were drilled at depths between 3 to 4.5 km and met temperatures ranging from 185"C to 330°C. The second project, at Camborne (UK), has been managed by the Camborne School of Mines (Baria R. et al., 1989 ; Parker R.H., 1989): three boreholes were drilled in the granite to depths of 2100 to 2600 m; maximum bottom temperatures reach 80"C. In both cases, monitoring the induced seismicity was very helpful in defining the stimulated regions, the reservoir growth and the complementary drilling program.